Re: [PATCH] livepatch: fix race between enabled_store() and klp_unregister_patch()

[Petr Mladek]

On Tue 2015-12-01 09:50:23, Jiri Slaby wrote:
> On 12/01/2015, 02:11 AM, Josh Poimboeuf wrote:
> > When I try to recreate something similar by putting a delay in
> > enabled_store(), klp_free_patch() just sleeps on its call to
> > kobject_put() until enabled_store() returns.  The unregister stack looks
> > like:
> > 
> >   [<ffffffff812e966b>] __kernfs_remove+0x1fb/0x380
> >   [<ffffffff812ea273>] kernfs_remove+0x23/0x40
> >   [<ffffffff812ec601>] sysfs_remove_dir+0x51/0x80
> >   [<ffffffff81407fb8>] kobject_del+0x18/0x50
> >   [<ffffffff8140804a>] kobject_release+0x5a/0x190
> >   [<ffffffff81407f27>] kobject_put+0x27/0x50
> 
> What about _put outside of klp_mutex in klp_unregister_patch (and maybe
> the other _put's as well)? Plus Li Bin's patch.

This might work. But I am pretty sure that we would need to put also
all the other kobject_puts outside of the lock.

I wondered how the approach with mutex_trylock() would look like
and got the patch below.

It is not trivial but it still might be easier than moving all
the kobject_put() calls. Also it should be easier to review
because all the logic is on a single place.

What do you think?